Rotary valves typically utilize a rotating plug or gate that often includes a hemispherical seating surface sized and arranged to bear against a seat ring positioned at the inlet of the valve's housing. Many plugs are located at an offset relative to the shaft so that the plug withdraws from the seat ring along a path rearwardly out of contact with the seat ring as it rotates from a closed position to an open position. It is important that the seat ring be accurately aligned relative to hemispherical plug to ensure a leak-free closure.
Side-to-side (lateral) alignment of the plug along the shaft can be accommodated simply by moving the plug or shaft axially to align the plug seating surface laterally relative to the seat ring. However, radial movement, transverse to the axial direction of the shaft, cannot easily be accomplished because the valve's housing/casing includes fixed bearing surfaces for the shaft that prevent any radial movement and the plug is radially fixed relative to the shaft. Accordingly, any inherent variations in the location of the plug's seating surface relative to the axis of rotation of the shaft can result in a gap between the seat ring and plug seating surface, causing leaks and binding of components during movement.
A technique for correcting misalignments between the seating surface of the plug and the seat ring is shown and described in U.S. Pat. No. 5,305,987 to Baumann. This patent teaches a plug mounted on a hub that it is adjustable so that the plug can be moved toward and away from the seat ring. In addition, the plug includes a ball and socket joint that allows a user to change the plug's angle of contact relative to the seat ring. These adjustments ensure the maintenance of a tight seal when the plug is placed in a shut-off position.
Additionally, the flow characteristics of fluid though a rotary valve are often of importance. When the plug is partially open, fluid entering the valve is under high pressure and forms a jet. This jet can generate noise, often in the form of a whistle. In most valves, the outlet is completely uncovered and, therefore, a substantial pressure drop occurs. In addition, flow patterns are disrupted by the presentation of a wide-open outlet resulting in further noise and, in many applications, cavitation. A more-balanced, low-noise flow through the valve housing is desirable.
It is, therefore, an object of one embodiment of this invention to provide a rotary valve having a simple and effective mechanism for providing an accurate fit between the plug's hemispherical seating surface and the seat ring. This adjustment mechanism should adjust easily over a relatively large range of distances. According to another embodiment of this invention, the rotary valve should provide a smooth flow characteristic through the housing and should have noise-reducing structures at the inlet and outlet.